Invisible aerial battles: how nocturnal butterflies try to outwit bats

Posted on Apr 29, 2022      35

There aren’t many good examples of two species embroiled in a massive battle for survival. Bats and nocturnal butterflies are just about the brightest of them all. These animals go after each other in their evolution, trying to find new tricks to win the eternal battle between predator and prey.

Bats first gained the ability to echolocate about 65 million years ago. They emit high-frequency “clicks” with their mouth or nose and then listen for echoes bouncing off objects. In this way, bats use sound to illuminate the world around them.

Thanks to echolocation, bats gain hunting advantages not available to other aerial predators. They hunt at night, which means they can chase and eat nocturnal insects.

This ability of bats has seriously endangered the insects that bats hunt - such as crickets, lacewings, grasshoppers and others. And many of these insects have developed many countermeasures that help them survive. Most noticeably, such countermeasures appear in noctuid moths.

Development of new organs

Many nocturnal moths have had to develop ears that are sensitive to echolocation clicks. Thanks to this completely new sensory organ for butterflies, they can hear that a bat is close. And avoid the attack - for example, hide in the foliage or fly away.

Some butterflies have even learned to make their own sounds, warning bats they are poisonous. The butterfly makes high-frequency clicks that a bat can hear. And the bats learn pretty quickly that the clicking butterfly is not tasty food. So they stop perceiving them as prey.

Some butterflies can make sounds that interrupt the echolocation clicks of bats. If their own clicks overlap with those of an approaching nocturnal predator, the butterflies can confuse the bat. And they become harder to catch.

The Chinese oak peacock-eyed butterfly has sound-absorbing wings that serve as acoustic camouflage

Sound Absorption

But how do butterflies that don’t have ears protect themselves? They had to develop passive protection. This means that the butterfly will have adaptations all the time, whether there is a bat nearby.

One option for this protection is acoustic camouflage. This is an audible version of visual camouflage. Visual camouflage, for example, is used by an octopus masquerading as a rock, or an insect masquerading as a leaf.

To hide from the sound, butterflies have specialized scales on their wings and body that absorb the sound energy emitted by bats. As a result, the sound echo from the butterfly’s body is muted. Thus, butterflies literally disappear from the sound picture of the night sky.

Studying the properties of the sound-absorbing scales of noctuid moths can be useful to humans as well. The same technique could be used for the walls of buildings near noisy roads or sound studios.

Examples of acoustic “tricks” in two different species of butterflies

Redirecting the attack

Another example of adaptation is acoustic “deceptions.” This is the sonic equivalent of the false “eyes” that can be seen in fish and daytime moths. Thanks to them, an attack of a predator is redirected from a vital part of the insect, like its head, to the winglets, which can be lost with little harm.

In butterflies, elongated, twisted formations at the ends of the wings become such “cheaters. Also, some butterflies have very long spurs on their hind wings, ending in twisted seals. With their help, butterflies reflect sound and redirect it at many angles. As a result, a bat is more likely to attack this outgrowth than the vulnerable body of the butterfly itself.

But it’s not just nocturnal moths that change. Scientists have found some evidence that bats change their echolocation signals to sneak up on butterflies that have ears. But it’s still unclear whether bats bypass acoustic camouflage.

Right now, it looks like the butterflies are winning the race for survival, but the bats probably have a few tricks in store.